Short Answer:

Planing is a machining process used to produce flat, smooth, or contoured surfaces on large workpieces. In this process, the workpiece moves back and forth under a stationary single-point cutting tool. Planing is mainly used for machining heavy and long parts that cannot be handled on a shaper or milling machine.

This process provides accurate and uniform surfaces on large components such as machine beds, slides, and tables. The planing machine operates on the same principle as shaping, but in planing, the workpiece reciprocates while the cutting tool remains stationary.

Detailed Explanation:

Planing

Planing is a fundamental machining operation in which a large workpiece is moved back and forth beneath a fixed cutting tool to produce a flat, plane, or contoured surface. It is commonly used in heavy engineering industries for machining long, wide, or heavy components that are difficult to process using other machines. The machine used for this operation is called a planer.

Unlike the shaping process, where the cutting tool moves and the workpiece remains fixed, in planing, the workpiece reciprocates while the cutting tool is stationary. This allows the machining of larger surfaces efficiently. The cutting tool removes metal during the forward stroke, while the return stroke is idle.

Working Principle of Planing

The working principle of planing is based on the reciprocating motion of the workpiece over a stationary cutting tool. The workpiece is rigidly fixed on a large table, which moves linearly back and forth under the cutting tool. The cutting action occurs only during the forward stroke, and no cutting happens during the return stroke.

After each stroke, the cutting tool moves slightly sideways to start a new cut adjacent to the previous one. This side feed continues until the entire surface of the workpiece is machined. The feed motion of the tool and the depth of cut are adjusted depending on the desired surface finish and accuracy.

The motion in planing can be divided into:

Primary motion (cutting motion): The reciprocating motion of the table carrying the workpiece.
Feed motion: The slow, lateral movement of the cutting tool after each stroke.

Main Parts of Planing Machine

Bed: The large and rigid base that supports the entire structure and ensures vibration-free operation.
Table: A heavy platform mounted on the bed that holds and reciprocates the workpiece during machining.
Column: Vertical supports on either side of the machine that carry the tool heads and guide rails.
Cross Rail: A horizontal beam connecting the two columns, providing vertical movement for the tool head.
Tool Head: Holds the cutting tool and allows adjustment of feed and depth of cut.
Driving Mechanism: Converts rotary motion from the motor into linear reciprocating motion for the table.

Types of Planing Machines

Double Housing Planer: The most common type, with two vertical columns supporting the cross rail and tool heads. Used for large, heavy workpieces.
Open Side Planer: Has only one housing, allowing machining of extra-wide workpieces.
Pit Type Planer: The table is fixed in a pit, and the tool head moves; suitable for very large jobs.
Edge Planer: Designed for machining the edges of plates and structural components.
Hydraulic Planer: Uses hydraulic power for smooth and adjustable motion of the table.

Applications of Planing

Machining large flat surfaces of machine beds and guideways.
Producing slots, grooves, and keyways in heavy components.
Finishing workpieces that require high accuracy and smoothness.
Used in repair workshops for reconditioning large parts.
Creating accurate surfaces on large castings and weldments.

Advantages of Planing

Suitable for large and heavy workpieces.
Provides accurate and smooth surfaces.
Can machine multiple surfaces at once using several tool heads.
More rigid and stable than shaping machines.
Can handle hard materials efficiently.

Limitations of Planing

Low production rate due to idle return stroke.
Requires more space and power than smaller machines.
High initial and maintenance cost.
Not suitable for small jobs or mass production.
Surface finish quality is lower compared to grinding or milling.

Conclusion

Planing is an essential machining process for producing accurate flat and contoured surfaces on large workpieces. It plays a vital role in heavy manufacturing industries where large components need precise machining. Although it has limitations such as slower operation and high space requirement, planing remains an effective method for heavy-duty and large-scale machining tasks. Its simplicity, accuracy, and ability to handle big jobs make it an important process in mechanical workshops.